Repeater selection for toll lines



April 16, 1929. E. VROOM ET AL REPEATER SELECTION FOR TOLL LINES Filed June 27, 1925 4' Sheets-Sheet 1 y WA/fy April 16, 1929.

E. VROOM ET AL.

REPEATER SELECTION FOR TOLL LINES Filed June 27, 1925 m e/zfwv'.

by J

4 Sheets-Sheet 2 fan dr/ Iran/27 .hrqafl 4. have! Affjz- April 16, 1929. E. VROOM ET AL REPEATER SELECTION FOR TOLL LINES Sheets-Sheet 5 Filed June 27, 1925 Awe/2mm" April 6, .1929. E. VROOM ET AL 1,708,982

REPEATER SELECTION FOR TOLL LINES Filed June 27, 1925 4 Sheets-Sheet 4 I l I by Affiz" Patented Apr. lti, l

UNITED STATES PATENT OFFICE.

EDW'JLRD VRQOM, F OSSINING, AND JQSEPl-I A. .KRECEK, 03E BRQOKLYN, NEVT ASYuItE-IiifilRSv TO \VEEETERN ELECTRIC GUMIANY, INCORPORATED, 6F NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

SELECTION FOR TOLL LINES.

Application filed June 2?, 1925. Serial No. 39,882.

This invention relates to a telephone exductors 105 and 106 and the right contact of change system and more particularly to the relay 116. Nomadjustable gain control zip-- automatic selection of speech amplifying; ap paratus in addition to network 186 is shown 5. paratus for toll line. 1 associated with the toll line conductors.

' Speech amplifying apparatus in the form Switches 149 and 159 are arranged to connect ofelectron tube repeaters make possible need a toll line with the apparatus of a repeater transmission over very long distances. They that has been selected by a cord circuit.- have also made possible the use of small gauge Fig. illustrates a toll cord circuit ar- 60 wire in cables for toll lines. The insertion ranged tor the welLlqnown functions of such 10 of repeaters in toll lines at interconnecting cord circuits, in addition to the function of stations has heretofore been accomplished by distinguishing between lines that require the manual methods and the repeater gain conaddition of apparatus "for speech amplificatrol apparatus has been adjusted by the same tions, and means for selecting a repeater to be 65 method. It has been found that this is not added in series with the line conductor for the most ellicient method of toll line control this speech amplification.

from a transmission viewpoint since it is dii'h- F 8 illustrates a toll line and repeater cult for operators to handle this apparatus in selec ion apparatus similar to Fig. 1.

a manner to obtain the best results. An error Fig. at illustrates electron tube repeater cir- 7 by an operator in the interconnection of toll writs of thctype completely disclosed in Patlines may resultin poor transmission which is cut No. 1,511,423 issued October 14:, 1924 to very annoying to the telephone subscriber. Donald A. Quarles et al.

It is the object of this invention to provide automatic selection of speech amplifying apparatus for toll lines that require speech am- Let it be assumed for the following descripplification which. is made possible by the use tion tha incoming and outgoing toll lines of apparatus for ascertaining the require interconnected by the cord circuit Fig. 2 rements of lines in addition to the use of nonquire the addition of a repeater Fig. i for adjustable repeater gain control apparatus speech amplification. Upon the initiation of so A. feature of this invention relates to the an incoming call over the toll line Fig. 1, re- 3U automatic selection of repeaters independent lay 137 is operated to light lamp 113 and of control by a switchboard operator, includoperate relay 111. A switchboard operator ing automatic discrimination between lines inserts plug-200 into jack 100 to answer the that require the addition of a repeater in incoming call. The operator ascertains the a; series with the talking conductor and lines line wanted and inserts plug 201 into jack 300, that do not require this addition. which it will be assumed is the wanted line.

A further tteature of: this invention relates The connection is thus completed by the operto the provision of means for the elimination ator, without regard as to whether the inserof contact resistance inthe repeater selection tion of a repeater is necessary. apparatus in order to stabilize line balance so Since the incoming line is of sufficient General description.

- that non-adjustable gain control apparatus length to require the addition of a repeater,

may be used. it is equipped with apparatus, as shown in Fig. 1 shows diagrammatically a toll line Fig 1, withthe exception of coruluctor 109.

l which may have either oi? two cha 'acteristics. When the cord circuit is associated with such One characteristic is that of a short toll line a line a marginal relay remains normal in that does not require the addition of a reorder that'another relay may be operated peater. This has the sleeve of j 10k conthrough its contacts to signify thata repeater nected directly to the winding of relay 112 is required tor the line. The outgoing line through conductors 105,109,21nd108. A sec- F 3 is also equipped with apparatus of such 100 end characteristic is that of a long toll line nature that the cord circuit apparatus asso- 50 that requires the addition of a repeater and ciated with plug 201 is able to distinguish behe s the sleeve of jack 100 connected to a high tween thisline and a line that does not require resistance winding of relay 114, through conthe addition of a repeater. When the cord Fig. 3

.idle repeater is selected by the cord circuit switch 259'and apparatus is operated to signity to one of the lines that a repeater has been selected. The apparatus of the line in is first actuated to hunt for the repeater selected by the cord circuit through the contacts of switches 3 19 and 359. Upon the selection of the repeater by apparatus of the line Fig; 3, apparatus ofthe line Fig. 1,

is actuated to associate this line with the oppositeend of the repeater. As soon as the lines a're'associated with the repeater, that has been selected by the'cord circuit, alternating current sources 371 and 135 are connected through the contacts of the switches 3 l985,91-19-159 and the contacts of re- 1ays'133 and 329 to eliminate any contact resistance in the form of a film, oxidization cor-dirt that may be on the surfaces of said contacts. A train of relays is operated as a time measuring device to allow the alternating current to flow through the above recited contacts for a predetermined time period. When the train of relays has operated the alternating currentsources are cut off.

A repeater has now been selected by the cord circuit and associated with the apparatus of Figs. .1 and 3 but has not as yet been associated with the line. As soon as the contact resistance has been eliminated from the contacts relays 117 and 328 are operated to insert the selected repeater in series with the line conductors and associated gain control apparatus. The operation of these relays separates thetoll line "from the cord circuit and tell line multiples,represented by jacks and 300. The'elimination of contact resistance ,in the manner described makes it possible to use a non-adjustable repeater gain control apparatus in the form of resistances. Diil'erent gain control apparatus may be required for each line to adjust all lines to approximately an equal quality of transmission.

The repeater is equipped with relays 432 and 433which may be operated over the line by ringing current. A circuit is established through the'contacts of these relays to actuate the supervisory signaling apparatus in the cord circuit. The switchboard operator may actuate a key to release relays 117 and 328 to reassociatethe toll lines with the cord circuit throughjack 100 and plug 200, also through jack 300 and plug 201. In this manner the operator ma'y supervise the lines in the standard manner for such operation For monitoring upon a connection the opera tor may actuate key 205 which is associated with the repeater circuit through contacts of relay 216.

An interconnection between a long toll line and a short toll line or local line does not require the insertion of a repeater. Therefore, upon the insertion of the cord circuit plugs into the line jacks, apparatus associated with the plug inserted in the jack of the long line may signify that a repeater is required, but the apparatus associated with the plug inserted in the jack of the short line will signify that a repeater is not required. When such an interconnection is made the apparatus of the cord circuit for selecting a repeater is not operated and does not interfere with the selection of repeaters by other cord circuits. The apparatus of the cord circuit for distinguishing the type of line with which the plug is associated accomplishes the result of associating repeaters only with lines that require speech current amplification.

Detailed description.

The invention having now been briefly described it will be assumed that a call is incoming over a toll line to a toll switchboard which is to be connected by a cord circuit to an outgoing toll line both lines being of sufticient length to require a repeater in circuit with the talking conductors.

The incoming toll line is connected to conductors 101 and 102 which are extended through the contacts of relay 117, conductors 103 and 1104, condenser 137, left contact of relay 112, and winding of relay 110. The ringing current impressed upon this tell line by a distant operator actuates relay 110, which in attracting its armature establishes a circuit to operate relay 111. The operai' ion of relay 111 establishes a locking circuit for itself and a circuit through the filament of lamp 113 to cause its illumination. Lamp 113 represents a particular toll line associated with jack 100 in the face of the switch board at which is located a plurality of cord circuits as shown in Fig. 2. The switchboard opcrator answers the call by inserting plug 200 in jack 100 in the usual manner.

Toll lincs of suflicient length to require a repeater in series with the talking conductors are equipped with relays 114, 115 and 110 as ociated with the sleeve comluctor of the jack and cut-oft relay oi the lini and connected as shown by conductors 105, 100, 107 and 108. Toll lines that are not of sufficient length to warrant the insertion of a repeater do not have such re ay equipment and the sleeve 01 the jack is connected from conductor through conductors 100 and 108 and the winding of cut-off relay 112.

Upon the insertion of plug 900 into jack a circuit is. established to operate sleeve relays which determine Whether a repeater is rctpiired for the incoming line. This circuit 'inay be traced from grounded battery, through the windings of relays 222 and 221, contact oil relay 2220,5l6856 of plug 200, sleeve oi jack 1:00, conductors and 106, right contact of relay 116, left Winding of relay 114 to ground. It will be noted that resistance connected to grounded battery is in multiple with relays 221 and 222 to form the proper marginal conditions for relay Relays 114;.and 221 operate in the circuit traced. llelay is marginal and does not operate in series with the high resistance Winding of relay 11-11. The marginal condi tion .t'or relay 222 is arranged so that when it is associated with a line that requires a repeater it remains unoperated in order that the operation of relay 22-1 l'lltlYCSbtLbllSl-l a circuit from ground through its left contact and the contact cit relay 222. to. operate relay 223. Relay 223 establishes a locking circuit for itself. through its left contact to the operating ground. The oporation of relay 22? also prepares thro 91h right outer contact, a part of the circuit to indi ate that a repeater is required for the connection. It, however, only indicates that a repeater is required. for the incoming toll line and as previously described it necessary that a repeater be required for both the incoming and outgoing toll lines to cause the actuation of the cord circuit repeater selecting apparatus. i

'lhe operation of relay 1L1 establishes an winding of relay 112. .-lie operation of relay 112 releases relay 111 and extingulshes lamp 113 and further opens through its right contact the circuit of the ring-up relay which is bridged across the toll line conductors. Clhe cutolf relay 1 12 remains operated during the connected periial o'l? the line. The opcratiitui ol? av 110 further establishes a low resistance Lll cult through the winding of relay This may be traced from ground, through the right Winding o'l relays 11 1 and 115, right contact of relay 110, conductors 1:06 and 105, sleeve of ack 100, sleeve of plug 200, contact of: relay 220, windings of relays 221 and llelay is new operated but ias no function at this time. The relays 114: and 115 are now maintained operated through this low resistancecircuit.

I The operator actuatcs talking key 206 at the time when. lamp 113. is lighted, to. associate the telephone circuit, represented by the smell rectangle 207, with the incoming toll line conductors in order to determine what line is Wanted. Let it be assumed that a toll line, Fig. 3, 0t suliicie'nt length to require a repeater desired by the calling line. T he operator therefore inserts plug 201 into jaclr 300. This line is equipped with. relays 315, 316 and 317 Which operate in the same manner as relays 114i, 115. and 110. A. circuit is thus established from ground through the high resistance winding ol: relay 315, left contact of relay 317, conductors 306 and 305, sleere of jack 300, sleeve of plug 201, rightcontact of relay 21S), windings or relays 218.

21 and 2.39 to grounded battery in niultiple with resistance 257 to grounded battery. llclays 230, 218 and 2:315 operate inv the circuit traced. Since it is a line that requires a repeater, relay 1.7 does not operate until the line slee c re tance has been reduced l the operation 0!. the line relays. The op-- elation o1" relay 21S establishes a circuit to operate relay 225 from grounded battery, ihrougl'r its winding, contact of relay 217, to around througlii the left contact 01'' relay 218. 'l he operation of relay completes an obvious locking circuit for itself through its right contact and a series circuit for the sclection of a repeater through its left outer contact which will be described later. The operation of relay 280 establishes an obvious circuit to energize relay 212. The energize.- tion of relay 212 establishes a circuit For bridging; the left winding 01' coil .36 and the Winding ol relay211 across the tip and ring coud. rs througlri alternate contacts, of key 20-1 Whenever thiskey perated after the lines-are connected. ".jllhe operation of this ltcy "for splitting the lines and this bridge is used to giveoperators supervision as is done in general practice for toll l' re control.

The operation oil relay 315 e: .ishes an obvious circuit to energize relay 316, through its right contact, and the cnergization of relay 2316 establishes an obvious circuit to energize relay 317. A circuit is now established from grounded battery, through resistance 370, right contacts. of relay 317, conductors 307 and 30S, wind ing of cut-off relay 311 to ground. The operation of relay 311 disassir ciates the rind-up relay 81.0 from the toll. line corull'lctors in order that it may be renmred to prevent transmission loss. A circuit is further established from ground through the low re istnnce left windings o1 relays 31:3 and 316, lelt contact of relay 317, conductors 300 and 305, sleeve of jack 300, sleeve of plug: 201, right contact of relay 219, Windinp oft relays 218, 217 and -39 to grounded battery. Relay 21.7 now operates in this low resistance circuit but serves no purpose at this time since relay 225 is maintained. in a locked circuit to ground through the left contact of relay 218.

The'initial circuit en'iployed'in the selection of a repeater to he placed in circuit with the incoming and outgoing toll lines, is established through the contacts of relays 223 and 225. This c rcuit may be traced from ground through the rightouter contact of relay 223 left outer contact of relay 225, right back contact of relay 2353, contact and winding or these'terminals through the normal contacts of relays 223 and 225 of the cord circuits not selecting repeaters, but is not connected to a terminal when relays 223 and 225 are operated and relay 23 1is not operated. In this manner the switch magnet 250 is energized when brush 251 'is'associated with'any terminal of the switch other than the terminal connected to the cord circuit in use and thus the brushes 251 and 252are rotated to conductors 260 and 261 where the switch brushes are arrested bythe absence of direct battery. Re

relays 228 and 229.

lay 230 is shunted during the time that brush 251 is associated with terminals connected to direct battery. It, however, operates as soon as the brush is associated with conductor 260. The operation of relay 230 establishes a locking circuit for itself throughresistance 258 to ground and an operating circuit for relay 229 from ground through its left outer contact, winding of relay 229- to grounded battery through the lett contact of relay 226.

The operation of relay 229 establishes an operating circuitfor relay 228 from grounded battery, through its winding, contact of relay 229 to ground through the right normal contact of relay 127. i

The locking circuit of relay 230 further associates ground through resistance 258 with resistance 258 and switch magnet 259. This prevents the operation of magnet 250 by other cord circuits served by switch 2&9 until a repeater has been selected'and this locking circuit released. In effect this is a cord lockout circuit arrangement. The cord circuits equipped for repeater interconnection are divided into groups with a number of cord circuits in each group. Each group is served by a switch the same as switch 249 and each cord circuit of the group is connected to a particular terminal of the switch. Each switch is served by a pair 01? relays such as This lock-out circuit serves each group of cord circuitsin such to remain in its normal position.

manner that only one cord circuit in a plurality of groups may select a repeater at any one time. The switch and its associated contacts and apparatus is known as a primary lock-out circuit and is served by the secondary lock-out circuit of which relays 228 and 229 serve part of a major group and relays 226 and 227 serve another part of the same major group. By this arrangement only one cord circuit of a major group may be in the process of repeater selection and interconnection at any one time. hen the interconnection of a repeater is completed by a cord circuit the primary and secondary lock-out circuits are released as hereinafter described thus allowing further selection of repeaters by other cord circuits in the group.

The operation of relay 228 associates ground, from the right contact of relay 127. with brush 252 and its associated contact. conductor 2G1 winding of relay 231, to grounded battery. Relay 127 is operated when all the repeaters are busy which operation prevents the completion of the circuit traced for relay 231. Let it be assumed that tie circuit for relay 231 is completed to cause its operation. The operation of this relay establishes a circuit from grounded battery through resistance 247, winding and contact of switch magnet 24-0, left contact of relay 231. winding of relay 232. left contact of relay 233 to brush 241 of switch 259. The brushes of this switch are shown in the selected position associated with an idle repeater circuit. If, however, brush 241 is resting upon one of the preceding terminals which is connected to a busy terminal characterized by ground. a circuit is established to energize switch magn vt 240 and relay 232 in series. The magnet and relay are energized in synchronism as the switch brush rotates over its associated contacts until brush 241 is associatwl with an idle repeater circuit which arrests the movement of the brush assembly and causes relay 232 Ground is now connected from the operating circuit f or relay 231 through its right contact, contact of relay 232, left winding of slow to operate relay 293 to grounded battery operating relay The operation of this relay connects ground through its left contact to brush 241 to make the terminal busy to other cord circuits which may hunt for idle repeater circuirs. The busy ground further establishes a circuit to operate relay 127 which may be traced through brush 21-1 and its associated contact. winding of relay 127 to grounded battery. The operation of relay 127 removes ground from the operating circuit of relay 231 to cause its release. It will be noted. however, that. a locking circuit is established for relay to maintain it in an operated position which circuit may be traced from grounded battery through its right winding and Contact, left outer Contact of relay 2'25 ltll Ill)

to ground through the right outer contact of a given number of lines. The trunks are relay Each cord circuit equipped with a switch sin'iilar to switch 259. Repeater circuits are connected to the terminals of these switches and are inultipled from switch to switch. vl hon the repeater has been selected by a cord circuit, relay 233 is operated as previously described to associate ground with the brush 241 so that the repeater associated with that circuit is made busy on all of the switches to which it is niiultipled. j

During the selection of a repeater by brush 2 1 it will be noted that the operation of relay 23d prevented by the continuous operation ot relay 232 in series with the switch magnet. delay 232 is extremely fast in its operation and relay 233 sluggish in its operation so that during; the released. moments of relay 232 there is not suilici'ent magnetism built up by the left winding of relay 2-33 to cause its operation. i

c it will be remembered that an operating circuit is established for relay 127 when an idle repeater is :lound. The operation of this relay establishes acircuit to operate relay 410 from grounded battery through its winding to ground throughthe right contact of relay 127. The operation of relay 410 closes the lilainent circuits of repeater tubes 451 and 401 from ground at the contact 0t relay 410, through the filament to the filament battery.

T he lockingcircuit traced for relay 233 turther establishes an i peii'a'tiii circuit for rela s 224- and 219 which ma 1 be traced. from 3 the right contact of relay 233 which is supplied with ground for its locking circuit, through the win dings of relays 2'24 and 219 to grounded battery. The operation of relay 22 i estaliilishes control circuits through its contacts which will be described as the con trol circuits are associated with the operating H'lci'lltllilffilll. The operation of relay 219 adds resistance 256 in series with the windings o f line relays 316 and 315 to cause the releaseof with the repeater that has been selected bythe cord circuit. It is however ordinarily iu-icessary for these switches to hunt for the selected repeater. There is one switch 349 for each toll line arranged for repeater selection. The switches 3 1-9 are connected to switches 359 by trunk conductors through relay 329. There is one relay 329 for each trunk and there are as many trunks as are necessary for the selection of repeaters by connected successively to the switch terminals around the arc and n'lultipled to all of the line switches similar to 349. a The switch may have any number of terminals associated with its brush nieinbers dependent upon the number of repeaters necessary for the line equipment of an oitice. Switch359 is arranged to select either end of a repeater arranged alternately upon the terminals of the switch. It is therefore apparent that a line may be used for an incoming or outgoing call. Plug 200 is always inserted in the jack associated with an incoming call and plug 201 is inserted in the jack of the outgoing called line. Switch 359 is arranged for both the east and west ends ot a repeater so that the incoming call. will al *ays get the same end of the repeater.

Let it be assumed that brush 341 is asso ci'ated with a trunk terminal characterized by a busy ground lroin the left inner contact of relay 325 in a line associated with a trunk and repeater similar to the lineshown in Fig. 3. The operation of relay 323 establishes a circuit to energize magnet 340 and relay 324 in series to rotate the brush assembly of switch 349 in search of an idle trunk. This circuitmay be traced from groiinded battery, through resistance 347, winding and contact of magnet 34:0, lett contact of relay 323. winding of relay 324:, left inner contact oi relay 325, brush S ll and associated contact, erminal and brush of a line switch similar to 349 that is connected to a busy trunk, to ground through the left inner contact of re lay 325 oi the line that is connected to said trunk. Magnet 340 and relay 3241: energize synchronously to advance the brushes oyer busy trunks. Upon the selection of an idle trunk relay 324 is released to establish an operating circuit for relay 325 from ground through the right contact of relay 323. normal contact oil? relay 324;, winding of relay 325 to grounded battery. Relay 327 is also operated in multiple with relay 325 through the right norinal contact of? relay 326. The oi'ieration of relay 327 associates alterhatiiu': current with lnrushes 343; 344;, 345 and 34-6 to prepare a 'iath through the contacts of to lay 329 when said relay is operated. The utility of the alternating current throileh the switch brush contacts will be described later. The operatioii of relay 325 associates ground through its left inner contact to brush 34-1 to hold the trunk busy so that it will not be selooted by other line switches similar to switch 34-9. This groulld is extended through the winding); of relay 320 to cause its operation. The circuit established through the left outer contact o-t relay 325 is not etflectiye at this time; Y 7

The operation of relay 320 establishes a circuit to energize switch magnet 350 in series with relay 321 to rotate the brush members of Ill) lll

not characterized by ground.

switch 359 in search of the repeater selected by the cord circuit. The terminals associated-with brush 351 are ail characterized by busy grounds from the lines or from the cord circuits except the one that'has been selected by the cord circuit for the lines in process of interconnection. The ground connection. to the terminals associated with brush 351 may be traced from the left inner normal contacts of relays 127 associated with cord circuits not in use and from the left inner contacts of relays 322 of lines that are already connected to repeater circuits.v It will be remembered that the relay 127 of the cord circuit being described is operated and thus the terminal associated with this cord circuit and-repeater The brush must now rotate until it is associated with the terminal characterized by the absence of ground. The circuit for energizing magnet 350 and relay 321 may be traced from grounded battery through resistance 357, winding and contact of magnet 350, left contact of relay 320, winding of relay 321, left inner normal contact of relay 322, brush 351 and thence to the busy ground connections previously described. The rotary movement of switch 359 is arrested when brush 351 is associated with the terminal not characterized by ground. The magnet 350 and relay 321 are deenergized and a circuit is thus established to energize relays 322 and 329 from ground through the right contact of relay 320, contact of relay 321 to grounded battery through the windings of these relays. The

operation of relay 322 associates ground through its inner contact with the brush 351 and its associated terminal to characterizesaid terminal as busy and to establish an operating circuit for-relays 130 and 220. These operating circuits may be traced from the switch terminal through the left outer contact of relay 127 to battery through the winding of relay 130 and to brush 2 16 and its associated terminal, right outer contact of relay 224 to grounded battery through the winding of relay 220. The circuits established by the operation of relays 130 and 220 will be described. later. 7

p The utility of the application of alternating current at a comparative high voltage, through the talking conductor contacts of switches 349 and 359 will now be described.

It is well known in the art that toll lines 'must be accurately balanced for good transmission and proper repeater efficiency. It

the contacts greatly vary, a manual adjustment of the gain control apparatus would be required. This is sometimes substituted by an automatic gain selection. It is a well known-fact that contact resistance exists especially upon rubbing contacts in the form of a film, oxidation or dirt. This resistance at times becomes very high. and is especially disruptive to electrical currents of low potent in]. An electrical current of high potential will however break down such a film or oxidation and obtain approximately a zero contact resistance between the surfaces of the contacts.

In order to eliminate this contact resistance alternating current of proper potential is carried through the switch contacts in the following manner: The application of: alternating current is made from source 371, through the contacts of relay 327, brushes 313, 344, 345 and 346 and their associated contacts, contacts of relay 329, brushes 353, 354, 355 and 356 and their associated contacts and thence through the windings of the output transformer and potentiometer of the repeater. The alternating current remains connected through these contacts for a period of time sufficient to eliminate contact resistance. It is then automatically cut off by the operation of relay 326, the operating circuit of which will be described upon the completion of the selection of the repeater by the calling toll line.

to 125 volts alternating current is found to satisfactorily reduce a very high resistance between contacts to a fraction of an ohm when applied to said contacts for one second. Resistance is placed in series with the contacts to bring about a current flow of approximately .015 ampere. It is also found that the current must be increased when direct current is used for cleaning purposes. 120 to 150 volts direct current may be used for cleaning the contacts in place of the lower voltage alternating current. The time duration for the application of direct current voltage is the same as for the alternating current voltage. Resistance is placed in series with the contacts to bring about a current flow of approximately .040 ampere. From the above the potential may be computed in accordance with the resistance of the medium between the contacts. It is not intended that the invention be limited to the use of the foregoing voltage and current "1111105 or the time given for its application to the contacts.

It will be remembered that relays 130 and 220 were operated upon the selection of the repeater by switch 359. The operation of relay 130 removes ground from the switch terminal associated with brush 151 to mark that terminal for the repeater selection in the same manner as previously described for brush 351 of switch 359. The operation of relay 220 adds resistance 255 in series with the line relays 114 and 1.15 in order to reduce the effective ampere turns for the n'iagnetization till ill)

oil relay 114 and cause its release. Relay 115, however, remains operated. A circuit isthus established to energize relay 122, from ground through the contact of relay 115, right normal contact 01 relay 114, winding of relay 122 to grounded battery.

The onergization of relay 122 establishes a circuit to energize magnet 140 in series with relay 121, if brush 141 is resting upon a busy trunk. Magnet 140 and relay 121 en ergize in a circuit from grounded battery, through resistance 17 3, winding and contact of magnet 140, right contact of relay 122, winding of relay 121, right inner contact of relay 120, brush 141 to busy grounds ciated with the switch terminals. Upon the location of an idle trunk the brush assembly is arrested and relay 121 released. A circuit is thus established. to energize relays and 118 over a circuit from ground, through the left contact of relay 122, contact of relay 121,

winding of relay 120 to grounded battery,

and through the left contact of relay 119, winding of relay 118 to grounded battery. The operation 01": relay 118 associates alternating current source 135 with the brushes of switch 149. The operation of relay120 associates a busy ground through its inner contact to brush 141 and its associated terminal. 'This busy ground further establishes a circuit to energize relay to establish an energizing circuit for switch 11mgnet 150. This circuit may be traced from grounded battery, through resistance 172, winding and contact of magnet 150, right contact of relay 125, winding of relay 124, right inner contact of relay 1.13, brush 151 to ground associated with all the terminals except the terminal shown connected to relay 130. The terminals over whichbrush 151 rotates are characterized by ground from the normal contact of relays similar to in other non-busy circuits and from ground through the inner contact of relays similar to 123 in other circuits that have selected repeaters. The brush assembly of switch 159 is thus rotated and relay 124 operated in synchronism with the operation of magnet 150 until the switch brushes are associated with therepeater that has been selected by the cord circuit. Relay 124 is then released to establish an operating circuit for relay 123 from ground, through the left contact of relay 125, contact of relay 124, winding of relay 123 to grounded battery. Relay 133 is also operated from the operating ground for relay 123 to associate the trunk talking conductors with brushes 153 to 156 inclusive of switch 159. The alternating cur- .rent from source 135 now passes through the switch contacts to eliminate contact resistance which may have become accumulated in the form of a film or oxidation. This alternating current passes through the output transformer and potentiometer of repeater 400 in the manner described for the elimination of contact resistance for switches 349 and 359.

The arrangement of the switches 149 and 159 with the associated trunks and repeater connection is the same as described for the switch arrangement in Fig. 3.

The operation of relay 123 associates ground through its inner contact with brush 151 to characterize the terminal upon which it rests with a ground to energize the magnets of other switches that may rotate in search of a selected repeater. This ground further establishes a circuit to ei'iergize relay 128 through the outer contact oil relay 130. Relays 234 and 216 are also energized from this ground or from ground associated with the outer contact of relay 123. This latter circuit may be traced from ground through the contacts of relays 432 and 433, outer con tact of relay 128, brush 244 and its associated terminal, lejft contact of relay 224, right inner contact and winding of relay 234 to grounded battery. The circuit for relay 216 extends in parallel from the inner contact of relay 234 througl'i the contact oil relay 238 to battery through the winding of relay 216. The operation of relay 234 establishes a locking circuit for itself through its right inner contact, left outer contact of relay to ground through the right outer contact of relay 223. The operation of relay 234 -turther associates grounded battery through its right outer contact with the contact of switch 249 that is associated with. brush 251. This direct battery releases relay 230 by shunting it, which in turn releases relays 228 and 229 to place the lock out circuit again in its normal condition for use by other cord circuits under its. control.

Relay 234 establishes a circuit through its left contact for supervision under the control of the repeater circuit. Previous to the operation of relay 234 a circuit is maintained from ground through the right contact of relay 221. left contact oi? relay 2341, contact of relay 210 to grounded battery through the winding of relay 213. The operation 01 relay 213 opens a circuit which would otherwise be established for the operation 01 relay 214 from grounded battery, through the contact of relay 213 to ground through the right contact of relay 221. The operation of relay 214 would establish an obvious operating circuit for relay 215 which would in turn establish a circuit from grounded battery through its left contact, filament of lamp 208 to ground to light this lamp. It will further be noted that the control of relay is now through the contact of relay 238 gizing circuit for relay 117.

tacts of relay 234. The'superyision is thus placed under the'control of the repeater circuits in order that the cord circuits maybe eliminated from the talking circuit conductors.

Theopera'tion of relay 128 further establishes a circuit to operate relay 131 from the ground connected to brush 151, through the outer contact of relay 139, inner contact of relay 128, left contact of relay 129, winding of relay 131 to battery. lay 131 establishes an'ol'n'ious operating circuit to energize relay 132. The operation of relay 132 establishes a circuit to energize relay 129 which operates and opens'the energizing circuit for relay 131 which releases in turn releasing relay 132. Relay 129 in operating further establishes a lockin g circuit for itself to the ground associated with switch brush 151. The operation of relays 131, 132 and 129 is for the purpose of allowing a period of time for the alternating current to flow through the brushcontacts of switches 349, 359, 1 19 and 159 to eliminate contact re sistance'. The operation of relay 129 prepares circuit paths to operate relays which cut off the alternating current'sources 371 and 135. A circuit is established to energize the windings of relays 126, 119 and 326 from ground, through the. right outer contact of relay 223, left outer contact ofrelay 225, right inner contact of relay 234, contact of relay 238, left contact of relay 214, right inner contact of relay 224k, brush 245 and its associated terminal, left normal contact of relay 132, right contact of relay 129 where the path is divided, one branch extending through brush 152 and its associated terminal, outer contact of relay 123, brush 142 and its associated terminal, outer contact of relay to grounded battery through the right winding of relay 119. The second branch of the circuit is extended through the winding of relay 126 to grounded battery to energize this relay. This path is further carried over conductor 171 to brush 352 and its associated terminal, outer contact of relay 322, brush 342 and its associated terminal, outer contact of relay 325 to grounded battery through the left Winding of relay 326. The operation of relay 119 opens the energizing circuit for relay 118 thus disestablishing the circuit from the alternating current source through the switch brushes. Relay 119 establishes a locking circuit for itself through its left is connected through the right outermost normal contact of relay 118 to establish an ener- The operation of relay 117 disassociates the line conductors T he operation of refrom jack 100 and the cord circuit and associates the line conductors directly through the repeater circuit. The operation of relay 117 further associates bridge 172 and network 136 with the repeater circuit.

The operation of relay 326 opens the energizing circuit for relay 327 to cause its release, which disassociates the alternating current source 371 from the switch brushes of switches 34:9 and 359. llclay 326 establishes a locking circuit for itself through its right winding and contact, contact of relay 32 t to ground through the right contact of rela 323. It further establishes a circuit throng 1 its left contact to associate bridge 373 with the outgoing toll line. The release of relay 327 establishes a circuit from the operating ground for relay 326 through its lcft outcrmost contact, winding of relay 328 to grounded battery. Relay 328 is operated to disassociate jack 300 and the cord circuit from the line conductors which are now associatcd directly with the repeatercircuit. The operation of relay 328 further associates bridge 372 and netwok 370 with the outgoing line and repeater circuit. The operation of relay 126 removes the short circuits from the potentiometers of the repeater.

The repeater, Fig. 4, has now been added in series with the talking conductors of the incoming and outgoing toll lines to make the proper transmission gain. This has bccn done automatically and independent of manual operation by the switchboard operator. The relays 432 and 433 in the repeater circuit control the lighting of cord circuit lamps and are operated by ringing current from a distant station in the usual manner of ringdown toll line service. Should the cord circuit signal be lighted the switchboard operator actuates a key in the usual manner which closes an obvious operating circuit through the winding of relay 238. The operation of relay 238 releases rcluys 117 and 328 in order that the toll lincs may be associated with the cord circuit for supervisimi. \Vhen the key is rcleascd to restore relay 238 to normal relays 117 and 3:28 are again operated over the circuits previously traced through the contact of relay 238.

It will be remembered that relay 216 was energized in parallel with relay 234 upon the relc; so of relay 238 at such time as the operator completed the connection of plugs 200 and 201 and restored the cord circuit keys to normal. Relay 216 in operating establishes a circuit path through the repeater circuit in order that the switchboard operator may associate the telephone circuit 207 through the contacts of key 205 with the line connection for monitoring purposes.

Let it now be assumed that a call is incoming upon the toll line represented by lamp 113 and jack 100 and that the cord cir- Ill) cuit plug 200 has been. inserted in jack 100. This line is of suflicient length to require a repeater in series with the talking conductors and a repeater will be selected it'the outgoing end of the cord circuit represented by plug-201 is inserted into a line of sufficientlength to require a repeater. If, however, the outgoing line is short, no repeater is required. For a connection between a long and a short line the dillerentiating means in the cord circuits must properly function so that a repeater is not selected.

Upon the insertion of plug 200 in the ack 100 relays 11a and 221 operate in the manner previously described. Relay 222 is marginal and remains normal since the energizing cir cuit is through the high resistance Winding of relay 114. Duringthe period of time that relay 222 remains normal a circuit is establisaed to energize relay 223 through its contact in the manner previously described. Itwill be remembered that the operation of relay Ila establishes an energizing circuit for relay 115 which in turn: establishes an energining circuit for relay 116. At this time the sleeve resistance is carried through low re sistance windings of relays 1.15 and 114 to cause the operation of relay 222. This sleeve resistance is reduced to a low resistance also tor the reason that a normal busy test condition must he maintained at the sleeve of jaclr 100.

Since it has been assumed that the line into which plug 201 is inserted is a short line it will not be arranged for repeater selection. Therefore, the sleeve circuit is carried through conductors 305, 309 and 308, winding of relay 311 to ground. The wind iug of relay 811 is the normal low resistance winding for such sleeve circuits. Upon the insertion of plug 201 into jack 300 a circuit is established from ground through the winding of relay 311, sleeve of jack 300, sleeve of plug 201, contact oi relay 21.9, windings of relays 218, 217 and 239 to grounded battery. All relays in the circuit traced nowoperate including themarginal relay 217, which re mains normal wl on the cord circuit is connected to a toll l] .e requiring the selection of a repeater. The immediate operation of relay 217 opens the operating. circuit for relay 225 to prevent the establishment of the series circuit previously described for actuating the lock out switch magnet 250.

It is apparent from the foregoing description that a repeater is only selected by an auton'is-itically differentiating cord circuit when it is required for both the incoming and outlines and since under this condition the lock out circuit is not energized there is no interference with other cord circuits that require the selection of a repeater.

The talhi conductors for toll connections that do not require a repeater are carried through the cord circuit key contacts and an ordinary toll cord circuit, which practice is well known in the art.

What is claimed is:

1. In a telephone exchange system, lines of different character, a cord circuitfor interconnecting said lines, and automatically operable means to distinguish a line that requires the addition oif a speech current amplifier.

2. In a telephone exchange system, lines of diiferent character, a cord circuit for interconnecting said lines, means for speech current amplification, and automatically operable means to distinguish lines that require amplification for speech current and to add said means for speech current amplification in series with said lines.

3. In a telephone exchange system, lines of different character, a cord circuit for interconnecting said lines, an electron tube repeater, and automatically operable means to distinguish lines that require the addition of an electron tube repeater.

4. In a telephone exchange system, lines of different lengths, a cord circuit for intcrconnecting said lines, repeaters and automatically operable means responsive to the interconnection of two longlines but unresponsive to the interconnection of two short lines to cause the interpolation of a repeater in series with said long lines.

5. In a telephone exchange system, lines of different character, a cord circuit for interconnecting said lines, repeaters and means in said cord circuit responsive to electrical conditions in said lines to cause the selection and connection of repeaters between certain of said lines. a.

G. In a telephone exchange system, lines of difi'erent lengths, cord circuits for interconnecting said lines, repeaters and means in said cord circuits responsive to the interconnection of two long lines to cause the interpolation of a repeater in series with said long lines, but unresponsive to the interconnection of a long and a short line to cause such interpolation. r

'i". In a telephone exchange system, lines of different character, cord circuits for interconnecting said lines, speech current amplifiers, means in said cord circuits responsive to elcctrical conditionsin said lines iior distinguishing between lines that require the addition of: speech current amplifiers and lines that do not require speech current amplifiers, and means actuated by said distinguishing means to select speech current amplifiers.

8. In a telephone exchange system. lines of dillerentcharacter, a cord circuit for interconnecting said lines, repeaters, means in said cord circuit responsive to electrical conditions n said l1nes for d1st1ngu1shing between lines that require the additlon of a repeater and lines that do not require this addition, means responsive to said distinguishmg means to select a repeater, and means perative upon the selection of a repeater to disconnect said cord circuit from said lines and'to interpose said repeater therebetween.

9. In a telephone exchange system, lines of different character, a cord circuit for interconnecting said lines, repeaters, means in said cord circuits responsive to electrical condit ons 1n sa1d lines for distinguishing between lines that require the addition of a repeater andlines that do not require this ad- (lltlGIl, mpans actuated by said distinguish mg means to select arepeater, and means operative only upon the selection of a'ropcat-er iO-(llSCODHGCi said cord circult from said lines and to lnterpose the selected repeater there- 7 between.

10. In a telephone exchange system, lines of different character terminating in jacks, cord circuits terminating in plugs,means actuated by the insertion of the plug of a 'cord circuit into a line jack to determine whether the line associated with said ]2LCl requires the addition of an amplifier for speech current. i

11. In a telephone exchange system, lines of difie'r'ent' character terminating in'jacks. cord'circuits terminating in plugs for interconnecting said lines, means actuated by the insertion of the plugs of a cord circuit into line jacks to determine Whether the lines associated with said jacks require amplification for speech cnrrent, speech current amplifiers, and means operable in accordance with said determining means to add speech current amplifiers in series with said lines; 7

' '12.In a telephone exchange system, lines of; different character, cord circuits for interconnecting said lines, means automatically operablein response to the interconnect-ion of lines to distinguish lines that require the addition of speechamplifying apparatus, a

common group of speech amplifying apparatus, and means responsive to said distinguishing means to cause the selection of an idle speech amplifying apparatus.

13. Ina telephone-exchange system, lines of clilierent character, cord circuits for interconnecting said lines, means automatically operable in response to-the interconnection of lines to distinguish lines that require the adedition of speech. amplifying apparatus, a

common group of speech an'iplifying apparatus, means resnonsiveto said distinguishmeansto cause the selection of an idle speech amplifying apparatus, and means responsive to saidselecting means to place said mplifying apparatus in series with said lines. 14-5111- a t eleph one exchange system, lines of different character cord circuits for inter- 7 connecting said lines, means automatically operable in response to the interconnection of lines to distinguish lines that require the ading means to cause the selection of an idle speech amplifying apparatus, and means responsive to said selecting, means to place said amplifying apparatus in series with said lines and to disconnect said cord circuit from said lines.

15. In a telephone exchange system, lines of different character, cord circuit for interconnecting said lines, means automatically operable in response to the interconnection of lines to distinguish lines that require the ad dition of speech amplifying apparatus, a common group of speech amplifying apparatus, means responsive to said distinguishing means to cause the selection of an idle speech amplifying apparatus and the interpolation of said apparatus between said lines, and means to prevent interference between selecting apparatus when a plurality of said interconnected lines require the addition of speech amplifying apparatus.

16. In a telephone exchange system, lines of diflerent character, cord circuits for interconnecting said lines, signals in said cord circuits, means automatically operable in response to the interconnection of lines to distinguish lines that require the addition of speech amplifying apparatus, a common group of speech al'i'iplifying apparatus, and means responsive to said distinguishing means to cause the selection of an idle speech amplifying apparatus, means responsive to said selecting means to place said amplifying apparatus in series with said lines and to disconnect said cord circuit, means in said amplifying apparatus responsive to signaling current over either of two interconnected lines to actuate the signal in said cord circuit, and means in said cord circuit to reassociate said lines with said cord circuit.

17. In a selecting circuit, apparatus contacts, means for variably coimccting together said apparatus contacts. a source of electrical current of sufiicient mtential to break down contact resistance between said contacts, means automatically operable for connecting said current source in a circuit through apparatus contacts connected together. means for maintaining said current through said circuit for a time period of sufiicient duration to eliminate resistance between the contacts so connected.

18. In a selecting circuit. paratus contacts having resistance in the 'orm of a film or oxidation over the surfaces of said contacts, means for variably connecting together said apparatus contacts, a source of electrical current of sufficient potential to break down such contact resistance, means automatically operable for connecting said current source in a circuit through apparatus contacts connected together, timing apparatus, means foroperating saidtimin r apparatus for maintaining said current through said circuit for a time period of sufiicient duration to eliminate resistance between the contacts so connected, and means for disconnecting said current source from said contacts at the termination of said time period. I

19. In a telephone exchange system, toll lines, repeaters, means to select repeaters ior saidlines, a gain control apparatus and net work in each of said lines to control the transmission. gain of said repeaters, apparatus contacts in said selecting means, the resistance between the surfaces 01. said contacts being such as to unbalance said lines and cause said gain control apparatus to be inelitcctive, a source of current of sullicient potential to break down said contact resistance, and means automatically operable to connect said current source through said apparatus contacts for a predetermined time period to break down said resistance and eliminate unbalance.

20. In a telephone exchange system, lines, speech current amplifying apparatus, means to select speech current amplifying apparatus for said lines, non-adjustable gain control apparatus in each of said lines, apparatus contacts in said selecting means, the resistance between the surfaces of said contacts beingsuch as to unbalance said lines and cause said non-adjustable gain control apparatus to be ineffective, a source of alter nating current of sufiicient potential to break down said contact resistance, and means to connect said. alternating current source through said apparatus contacts for a predetermined time period to break down said resistance and eliminate unbalance.

2-1. In a telephone exchange system,lines of ditl'erent character, a cord circuit for interconnecting said lines, repeaters, means in said cord circuit responsive to electrical con ditions in said lines to cause the selection of an idle repeater, and means operative upon the selection oi a repeater to connect each of said interconnected lines with said repeater.

22. In a telephone exchange system, lines able for passing said current through said contacts for predetermined period of time of sullicient duration toeliminate said contact resistance, and means to maintain said conductors disconnected :trom said contacts during the elimination oi said contact resistance.

2a. In an electrically operable system for interconnecting conductors, apparatus contacts, means for selectively positioning said contacts for interconnecting said conductors, contact resistance existing between said con tacts as positioned, a source of electrical current of sullicicnt potential to eliminate said contact resistance, means automatically operable for passing; said current through said contacts for a predetern'iined period of time of sutlicient dmration to eliminate said contact resistance, means to maintain said conductors disconnected tromsaid contacts during the elimination 01 said contact resistance, means operable at the termination of said time period for disconnecting said current source from said contacts, and means operable in response to the operation oi said disconnecting means to connect said con- 'ductors to said contacts.

25. In. a telephone exchange system, lines, repeaters, means for interconnecting said lines, and means automatically operable in response to said interconnection to distinguish lines that require the addition of a repeater.

26. In a telephone exchange system, lines, repeaters, means for interconnecting said lines, means automatically operable in response to said interconnection to distinguish lines that require the addition of a repeater and to add a repeater in series with said lines.

27. In a telephone exchange system, lines, repeaters, means for interconnecting said lines, means automatically operable in response to said interconnection to distinguish lines that require the addition of a repeater, and means actuated by said distinguishing means to select a repeater for said lines.

28. In a telephone exchange system, lines, repeaters, means for interconnecting said lines, and means automatically operable in response to said interconnect-ion to distinguish lines that require the addition of a re peater and lines that do not require such addition.

29. In a telephone exchange system, lines, repeaters, means for interconnecting said lines, means automatically operable in re sponsc to said interconnect-ion to distinguish lines that require the addition of a repeater and lines that do not require such addition, and means to select a repeater for lines requiring such addition.

30. In a telephone exchange system, lines of different lengths, repeaters, means for interconnecting said lines, and means autoniatically operable in response-to s. id interconnection to distinguish lines of a length that require the addition of a repeater.

, 31. Ina telephone exchange system, lines,

5 a rou of re eaters-common to said lines means for interconnecting said lines, means automatically operable in response to said interconnection t0 dlstinguishllnes that re- 

